External Radiation

The specific gamma ray constant for Tc99m is 5.4 microcoulombs/kg-MBq-hr (0.78R/mCi-hr) at 1cm. The first half value layer is 0.017cm of lead (Pb). Relative attenuation of the radiation emitted by this radionuclide results from the interposition of various thicknesses of Pb. The corresponding attenuation is shown in Table 2. To facilitate control of the radiation exposure from MBq (mCi) amounts of this radionuclide, a 0.25 cm thickness of Pb will attenuate the radiation by a factor of 1,000.

To correct for the physical decay of this radionuclide, the fractions that remain at selected time intervals after the time of calibration are shown in Table 3.

General

Neurolite®, Kit for the Preparation of Technetium Tc99m Bicisate for Injection forms a stable, lipophilic complex which can cross the blood brain barrier. Technetium Tc99m Bicisate crosses intact cell membranes and the intact blood brain barrier by passive diffusion. Five percent of the injected dose remains in the blood at one hour. The amount of Technetium Tc99m Bicisate in the brain is stable until about 6 hours. After background clearance, images of the brain can be obtained from 10 minutes to 6 hours after injection. Optimal images occur 30-60 minutes after injection. Technetium Tc99m Bicisate is cleared primarily by the kidneys.

Pharmacokinetics

In a study in 16 normals (13 men and 3 women, mean age of 31 ± 10 years; mean weight of 72 ± 11 kg), the pharmacokinetic profile in blood best fits a three compartment model with half-lives of 43 seconds, 49.5 minutes and 533 minutes. The highest concentration of radioactivity measured in blood was found at 0.5 minutes after intravenous injection and was 13.9% of the injected dose. Technetium Tc99m Bicisate and its major metabolites are not protein-bound.

Metabolism

Technetium Tc99m Bicisate is metabolized by endogenous enzymes to the mono- and di-acids of Technetium Tc99m Bicisate that can be detected in blood and urine. No studies have been performed to compare the concentration of Technetium Tc99m Bicisate or its metabolites in normal, ischemic and infarcted cells.

Technetium Tc99m Bicisate is excreted primarily through the kidneys. Within two hours, 50% of the injected dose is excreted and by 24 hours, 74% is found in urine. It is not known whether the parent drug molecule or its metabolites are dialyzable. Fecal excretion accounts for 12.5% of the injected dose after 48 hours.

Pharmacodynamics

Localization of the parent compound in the brain in part depends upon both perfusion of the region and uptake of Technetium Tc99m Bicisate by the cell. Once in the brain cells, the parent compound is metabolized to polar, less diffusible compounds. Studies in 21 normal volunteers show cellular uptake of 4.8-6.5% of the injected dose at five minutes after injection. The degree of cell function or viability needed for uptake is not known. The degree of cell function or viability needed for metabolism of the parent compound to the less diffusible compounds has not been determined. The likelihood that the metabolic pathway is damaged by ischemia is not known. Whether or not and to what extent uptake correlates with viability or function is not known.

The pharmacodynamics of Neurolite have not been evaluated for differences associated with age, gender, weight and liver or renal impairment. It is not known whether dosage adjustments for these factors are needed.

Clinical Trials

Two clinical trials were performed in a total of 359 subjects (273 with stroke, 86 normal). Of these 56% were men and 44% were women. The mean age was 60.2 years (range 23 to 92 years). Subjects were 87.2% Caucasian, 8.4% Black, 2.2% Hispanic, 1.7% Oriental and 0.6% other.

Eligible patients had a confirmed stroke. Patients with other brain lesions were not evaluated. Subjects received Neurolite (mean dose range 10-30mCi) and underwent SPECT imaging and either CT or MRI scans within 0-30 days of the onset of signs and symptoms of stroke. CT or MRI and the administration of Neurolite occurred at different and variable times after the onset of a stroke. The effect of the timing on the accuracy of the images cannot be evaluated. The Neurolite scan results were blindly compared to unblinded CT/MRI results, the short standardized neurologic examination (SSNE) and the final diagnosis (e.g., the overall combined clinical impression with CT/MRI and SSNE).

In these studies, at least one of three blinded readers made a diagnosis of stroke in 190 (85%) of the Neurolite SPECT studies and in 238 (88%) CT/MRI studies. The Neurolite and CT/MRI imaging results versus the SSNE and final diagnosis were comparable. Neurolite had 11 false positive and 34 false negatives. CT/MRI had 0 false positive and 31 false negatives. Both Neurolite and CT/MRI missed strokes (true positives) that were identified by the other modality. The majority of the false negatives in either modality were within 15 days of the clinical stroke.

The trials were not designed to determine when Neurolite or CT/MRI studies could become positive in relationship to the time of the stroke. The relevance of the Neurolite scan results to the prediction of neurologic function or brain cell viability is not known. Also, not known is the ability of the Neurolite findings to distinguish between a stroke and pre-existing CNS lesions. Neurolite should not be used for these purposes. (See Pharmacodynamics Section).

General

USE WITH CAUTION IN PATIENTS WITH RENAL OR HEPATIC IMPAIRMENT. TECHNETIUM Tc99m BICISATE IS ELIMINATED PRIMARILY BY RENAL EXCRETION. WHETHER TECHNETIUM Tc99m BICISATE IS DIALYZABLE IS NOT KNOWN. DOSE ADJUSTMENTS IN PATIENTS WITH RENAL OR HEPATIC IMPAIRMENT HAVE NOT BEEN STUDIED.

Patients should be encouraged to drink fluids and to void frequently during the 2-6 hours immediately after injection to minimize radiation dose to the bladder and other target organs.

Contents of the vials are intended only for use in the preparation of Technetium Tc99m Bicisate and are not to be administered directly to the patient without first undergoing the preparation procedure.

The contents of each vial are sterile and non-pyrogenic. To maintain sterility, aseptic technique must be used during all operations in the manipulations and administration of Neurolite.

Technetium Tc99m Bicisate should be used within six hours of the time of preparation.

As with any other radioactive material, appropriate shielding should be used to avoid unnecessary radiation exposure to the patient, occupational workers, and other people.

Radiopharmaceuticals should be used only by physicians who are qualified by specific training in the safe use and handling of radionuclides.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Studies have not been conducted to evaluate carcinogenic potential or effects on fertility. When tested in vitro, Neurolite prepared with decayed generator eluate induced unscheduled DNA synthesis in rat hepatocytes and caused an increased frequency of sister chromatid exchanges in CHO cells; but, it did not induce chromosome aberrations in human lymphocytes or cause gene mutations in the Ames test or in a CHO/HGPRT test. Unreacted bicisate dihydrochloride increased the apparent rate of gene mutation of the TA 97a strain of S. typhimurium in the Ames test; but, it did not demonstrate clastogenic activity in an in vivo micronucleus assay in mice.

Pregnancy: Teratogenic Effects

Animal reproduction studies have not been conducted with Technetium Tc99m Bicisate. It is also not known whether Technetium Tc99m Bicisate can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Therefore, Technetium Tc99m Bicisate should not be administered to a pregnant woman unless the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

Technetium Tc99m Pertechnetate can be excreted in human milk. Therefore, formula should be substituted for breast milk until the technetium has cleared from the body of the nursing woman.

Pediatric Use

Safety and effectiveness in the pediatric population has not been established.

Geriatric Use

Of 808 patients in clinical studies of NEUROLITE®, 421 patients were 65 or older and 190 were 75 or older. Based on the evaluation of the frequency of adverse events and review of vital signs and laboratory data, no overall differences in safety were observed between these subjects and younger subjects. Although reported clinical experience has not identified differences in response between elderly and younger patients, greater sensitivity of some older individuals cannot be ruled out.

NEUROLITE® is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to assess renal function prior to administration.

Materials for TLC Procedure

   Bakerflex silica gel IB-F, 2.5 x 7.5cm, Baker #4463-02
   Solvent system: Ethyl Acetate, HPLC grade
   Dose calibrator or gamma counter for measuring radioactivity
   Small chromatographic developing tank
   Syringe and shielded vials, as needed

TLC Procedure

Establish the radiochemical purity (RCP) of the final solution by the thin layer chromatography (TLC) using Baker-Flex silica gel IB-F plates and a solvent system of ethyl acetate. The RCP should be ≥90%.